Astrophysics/Black Holes

QuestionSo, not a nuclear question but thought I would ask anyway. So we know that black holes form when a star collapses in on itself once it no longer has enough fuel to hold against its own gravity. My question is, if this is how they form, where did super-massive black holes such as Sagittarius A come from? How did they form? And has anyone ever postulated that maybe after the big bang when the universe was a giant cloud of gas that maybe stars formed that would make Canis Majoris look like a BB which collapsed into these super-massive black holes?

AnswerI believe the consensus is that super-massive black holes are formed by accretion. Either by the absorption of other black holes or simple accretion of matter from nearby stars. Stellar density at the center of each galaxy (which is where these very large black holes are found) is way higher than it is out in the rim, during galactic formation a lot of things probably came by which were gobbled up. Also, black holes may be tiny if they're just the minimum mass to form via standard theories of stellar collapse, but their radius depends linearly on their mass and not on the cube root of their mass the way a solid object would. So these very large black holes grow to enormous sizes, making the process of absorbing huge amounts of matter a somewhat runaway one until they've cleared out their local sector.

Expertise

Fusion, solar flares, cosmic rays, radiation in space, and stellar physics questions. Generally, nuclear-related astrophysics, but I can usually point you in the right direction if it's not nuclear-related or if it's nuclear but not astrophysics.

Experience

Just moved from being a physics professor at the University of Texas of the Permian Basin into government work. Doctoral dissertation was on a reaction in CNO-cycle fusion, worked in gamma-ray astronomy in the space science division of the naval research laboratory in the high-energy space environment branch.

OrganizationsGovernment work as a physical scientist with a nuclear focus.

Education/CredentialsPh.D. in physics, research was on nuclear fusion reactions important in stellar fusion, further work on space telescope technology.